1. Field of the Invention
The present invention relates to a cleaning apparatus and a cleaning method, and more specifically to a cleaning apparatus and a cleaning method which can remove contaminants deposited on a treated body such as a substrate, particularly which can efficiently remove contaminants by efficient use of cleaning water.
2. Related Background Art
Semiconductor devices such as photovoltaic devices are generally apt to be damaged when polluted, and therefore, production procedures therefor must be arranged not only to prevent small dust particles or ion components, which are some types of pollutants, from adhering to the devices, but also to remove them to the utmost if necessary.
However, indiscriminately using a lot of cleaning water in order to obtain clean substrates or treated surfaces will result in increasing the cost of cleaning water, enlarging waste water treatment facilities, and increasing the treatment cost, which will in turn increase the fabrication cost.
On the other hand, and attempt to clean the devices with a small amount of cleaning water would result in insufficient removal of the above dust particles or ion components, thus raising possibilities of causing defects, which were not expected originally, and lowering long-term reliability due to unremovable ion components.
A variety of ideas have been presented heretofore to meet the above conflicting demands.
For example, there are generally used cleaning apparatuses, as shown in FIG. 1, having cleaning baths of the so-called cascade type provided with a plurality of cleaning zones and arranged to use a liquid already used for cleaning in a rear stage, for cleaning in a front stage.
In FIG. 1, reference numerals 901, 902, 903 designate first, second, and third cleaning liquid baths. A new cleaning liquid 904 is supplied through a supply pipe 904 to pour down through a shower 905 above the third cleaning liquid bath 903, then to clean a surface of substrate 907 as a treated body, and thereafter to be collected in the cleaning liquid bath 903 (as a primary treatment liquid 908). During this period, the substrate 907 mounted on a carry conveyor 906 is carried to the right on the plane of the drawing. Namely, the new cleaning liquid supplied through the supply pipe 904 is used for finish cleaning. The primary treatment liquid 908 collected in the third cleaning liquid bath 903 is fed by a pump 909 through a pipe 911, one end of which is connected to the third cleaning liquid bath 903, to a shower 910 installed above the second cleaning liquid bath 902, which is a front-stage cleaning bath. Thus, the substrate 907 is cleaned with the cleaning liquid before the aforementioned treatment.
The cleaning liquid used for cleaning herein and including contaminants is collected as a secondary treatment liquid 912 in the second cleaning liquid bath 902.
In the cleaning apparatus shown in FIG. 1, the secondary treatment liquid 912 in the second cleaning liquid bath 902 is fed by a pump 914 through a pipe 913 to a shower 915, whereby the substrate 907 is cleaned with the secondary treatment liquid 912. The cleaning liquid after cleaning (tertiary treatment liquid 916) is collected in the first cleaning liquid bath 901 to be disposed of.
Observing the treatment with respect to the substrate, it is arranged to transfer the substrate from cleaning with the cleaning liquid of a high degree of pollution to cleaning with cleaning liquids of gradually increasing cleanliness, thus being designed to achieve high cleaning effects with a relatively small amount of cleaning liquid.
It is apparent in this case that if the cleaning liquid is supplied at V 1/min to the final-stage cleaning liquid bath, shower rates at the first, second, and third cleaning liquid baths, then a waste rate from the first cleaning liquid bath is also substantially V 1/min.
For the above-stated cleaning method to achieve the intended purpose, it is, however, necessary that contaminants on the substrate quickly diffuse into the cleaning liquid with jet spray of the cleaning liquid.
There are cases where satisfactory cleaning cannot be made by the previously described method if the contaminants on the substrate are sticky or are layered in some thickness or if the contaminants are unlikely to diffuse into the cleaning liquid.
For throughly removing the contaminants of the above-mentioned types, there are methods to use a lot of cleaning liquid for cleaning at the position corresponding to the first cleaning liquid bath 901 where the substrate is first cleaned.
A first method among them is one to increase an amount of the cleaning liquid for the cleaning treatment corresponding to the first cleaning liquid bath 901, that is, to add a new cleaning liquid (for example, at a using rate V') to the cleaning liquid used for the cleaning treatment corresponding to the first cleaning liquid bath 901. A second method is one to increase the using rate V of the entire cleaning liquid. Either of the two methods inevitably increases the total amount of the cleaning liquid necessary for cleaning. This increase of the amount of cleaning liquid will result in not only increasing the supply demand of pure water or the like and increasing the production cost, but also increasing the demand of disposal facilities, increasing the disposal cost, and increasing feed capacity (pump demand etc.) of cleaning liquid. As a result, the cost for an apparatus increases, which could affect the product cost of devices.